Previous experiments on human and rodent mammary tissues have demonstrated that carcinomas and hyperplastic lesions at high risk of neoplastic transformation show a high frequency of angiogenic response. Other reports have indicated that the interstitial fluid of tumors in vivo has a strong angiogenic activity. Present attempts aim at: 1) Isolating the angiogenesis factor(s) in the tumor interstitial fluid and 2) developing an RIA for the factor(s) as a tool for detecting high tendency to neoplastic transformation in lesions morphologically not suspect.